OBJECTIVE: To report the clinical and mitochondrial genetic analyses of two families, each of which carries both the 11778 and 14484 Leber hereditary optic neuropathy (LHON) mutations in mitochondrial DNA. METHODS: In addition to detailed clinical histories, the complete sequence of the mitochondrial DNA (mtDNA) from each family was determined. RESULTS: A small Australian LHON family (Vic20) and a family from the United States carry the 11778 and 14484 LHON mutations...